1. Field of the Invention
The present invention relates to integrated electrical circuit components adapted to surface mount technology. More particularly, the present invention relates to an integrated device including overcurrent protection to a supply line as well as overvoltage protection and common-mode filtering to data lines at a data bus interface.
2. Introduction to the Invention
With the advent of digital signal processing and transmission, high speed data buses are required to interconnect computers and computer peripherals such as printers to consumer electronics products such as camcorders, VCRs, TVs, set top boxes and digital cameras. One standard bus convention is known as the IEEE 1394 multimedia connection. This particular bus convention employs two high speed differential twisted-pair data cables operating at a data transfer rate of 400 MBits/sec., or greater. It is very common for IEEE 1394 bus terminations at each device to require a common-mode filter by which common-mode noise and interference is removed from each differential pair. Another standard interface bus is the Universal Serial Bus (USB). The USB standard bus structure uses a single differential twisted pair data path for transferring data at high speed. As with the IEEE 1394 standard bus, USB terminations at each connected device can require a common-mode filter by which common-mode noise and interference is removed from the single differential pair. Another similar standard interface bus is the IEEE 802.3af powered Ethernet interface. This interface transmits both data and DC power over differential data pairs. It typically utilizes common-mode filters, overcurrent protection, and overvoltage protection.
Conventionally, a common-mode filter may be implemented as a broadband transformer comprised of two or more windings upon a ferrite core. For the IEEE 1394 bus termination the common-mode filter has comprised two pairs of windings wound through a ferrite core defining two longitudinal channels or apertures, for example. Common-mode filters of this type have typically been implemented as a component having a header for anchoring the core and a lead frame for providing connections to the windings. This filter component of the prior art typically also had soldering leads or pads enabling surface mounting and connection to a printed circuit board of the consumer device or appliance. One commercially available example of a stand-alone common-mode filter choke including a core-anchoring header and a connection lead frame for USB applications is the model C9513L common-mode choke available from CoEv, Inc., a unit of Tyco Electronics Corporation, assignee of this patent. This particular component includes a ferrite core and provides a 6 dB common-mode rolloff at approximately 60 MHz, while attenuating the differential data signal less than 1 dB at the same frequency.
Many standardized bus structures, including the IEEE 1394 serial bus, the USB serial bus, and “powered Ethernet” (e.g. IEEE 802.3af and similar technologies) as examples, provide for an on-cable power line in order to supply power to operate peripherals and network devices and circuits such as hard drives, keyboards, mice, DVD players, and computers, and/or to keep the physical layer of a device running while that particular appliance or device has its primary power supply turned off, so that the particular appliance or device can continue to identify itself and report its status to other devices and hosts on the network in order to minimize user complaints, for example.
In the IEEE 1394 bus structure, as with many other powered bus structures, overcurrent protection must also be provided. One particularly satisfactory way to provide overcurrent protection is to employ a polymeric positive temperature coefficient (PPTC) resistor, such as a PolySwitch™ PPTC resistor provided by the Raychem Circuit Protection division of Tyco Electronics Corporation, assignee of the present invention. The use of such PPTC devices within the IEEE 1394 bus structure, is described in “Meeting IEEE 1394 Overcurrent Protection Requirements Using PolySwitch Devices”, authored by Adrian Mikolajczak, Tyco Electronics Corporation, May 1, 2001, the disclosure thereof being incorporated herein by reference for all purposes.
Positive temperature coefficient (PTC) circuit protection devices are well known. The device is placed in series with a load, and under normal operating conditions is in a low temperature, low electrical resistance state. However, if the current through the PTC device increases excessively and/or the ambient temperature around the PTC device increases excessively, and if either condition is maintained for sufficient time, then the PTC device will become “tripped”, i.e., converted to a high temperature, high electrical resistance state such that the current flowing through the device is reduced substantially. Generally, the PTC device will remain in the tripped state, even if the current and/or temperature return to normal levels, until the PTC device has been disconnected from the power source and allowed to cool. Particularly useful PTC devices contain a PTC element which is composed of a PTC conductive polymer, i.e. a composition which comprises (1) an organic polymer, and (2) a particulate conductive filler, preferably carbon black, metal, and/or a conductive inorganic filler, e.g. a ceramic oxide or a metal carbide, nitride or boride such as titanium carbide, which is dispersed, or otherwise distributed, in the polymer. PTC conductive polymers and devices containing them are described, for example, in U.S. Pat. No. 4,237,441 (van Konynenburg et al.), U.S. Pat. No. 4,238,812 (Middleman et al.), U.S. Pat. No. 4,315,237 (Middleman et al.), U.S. Pat. No. 4,317,027 (Middleman et al.), U.S. Pat. No. 4,426,633 (Taylor), U.S. Pat. No. 4,545,926 (Fouts et al.), U.S. Pat. No. 4,689,475 (Matthiesen), U.S. Pat. No. 4,724,417 (Au et al.), U.S. Pat. No. 4,774,024 (Deep et al.), U.S. Pat. No. 4,780,598 (Fahey et al.), U.S. Pat. No. 4,800,253 (Kleiner et al.), U.S. Pat. No. 4,845,838 (Jacobs et al.), U.S. Pat. No. 4,859,836 (Lunk et al.), U.S. Pat. No. 4,907,340 (Fang et al.), U.S. Pat. No. 4,924,074 (Fang et al.), U.S. Pat. No. 4,935,156 (van Konynenburg et al.), U.S. Pat. No. 5,049,850 (Evans et al.), U.S. Pat. No. 5,378,407 (Chandler et al.), U.S. Pat. No. 5,852,397 (Chan et al.), U.S. Pat. No. 6,130,597 (Toth et al.), U.S. Pat. No. 6,300,859 (Myong et al.) and U.S. Pat. No. 6,392,528 (Myong), for example, the disclosures of which are incorporated herein by reference for all purposes. Ceramic PTC materials are also well known in the art. Negative temperature coefficient (NTC) circuit protection devices containing ceramic NTC materials are also well known in the art. For example, U.S. Pat. No. 6,300,859 (Myong et al.) describes a multi-layer circuit protection device including a layer of polymeric positive temperature coefficient resistance material sandwiched between conductive foil layers. An insulating layer is also described.
One of the problems and drawbacks of the prior art has been that the overcurrent protection device and the common-mode rejection filter, although both needed, have been separate components and have taken up valuable printed circuit board space within devices and appliances implementing powered high speed buses such as IEEE 1394, USB, or Powered Ethernet. An example of the prior art is shown in the FIG. 1 circuit schematic. Therein, an IEEE 1394 bus interface circuit 10 at a device or appliance includes an interface IC chip 12 implementing two IEEE 1394 channels feeding to two standardized 6-pin connectors 14 and 16. Power from a source 18 is passed to a power pin of connector 14 through a PPTC resistor overcurrent protection device 20. Power from the source 18 is also passed to a power pin of connector 16 through a second PPTC resistor overcurrent protection device 22. Separately, as shown in FIG. 1, two common-mode noise rejection filters 24 and 26 are provided between the channel chip 12 and each connector 14, 16 of the IEEE 1394 interface. The PPTC devices 20 and 22 and the filters 24 and 26 are separately mounted to a circuit board of the circuit 10 at the vicinity of connectors 14 and 16.
Another example of the prior art is presented in FIG. 2. Therein, a USB interface circuit 11 includes a USB interface chip 13, and two standard USB interface four-pin connectors 15 and 17. Power from a source 19 is passed to parallel-connected power pins of connectors 15 and 17 through a single PPTC resistor overcurrent protection device 21. The USB interface circuit 11 provides separate differential data pairs to each connector through a single conventional common-mode rejection filter 23. As with the IEEE 1394 example, in the USB example of FIG. 2, the PPTC resistor 21 and filter 23 are separately mounted to a host circuit board providing the USB interface.
In some implementations or a powered data bus, the designer may require additional overvoltage protection on the data and power lines to protect against undesirable and potentially damaging ESD and overvoltage surges. Typical overvoltage protection devices include TVS diodes, zener diodes, spark gap polymer materials, or other spark gap concepts. These overvoltage/ESD protection devices are typically located on the data lines, between the common mode choke and the I/O connector, or on the power line between the PPTC and the I/O connector. These are well understood in the art.
A hitherto unsolved need has arisen to provide a single, integrated device (e.g. a signal conditioning device) which combines a common-mode filter element with an overcurrent protection element and/or an over voltage protection element, thereby to save valuable printed circuit board room, to reduce component count and costs, and to reduce assembly costs otherwise associated with the particular appliance or device.